The present invention relates to cold weather footwear and particularly relates to footwear which has improved thermal insulation, moisture vapor transmission, wind resistance and water repellency characteristics.
In extremely cold conditions, the most important requirements for footwear in order to provide protection and/or comfort to the wearer are the reduction of heat loss from the foot and lower extremities and the controlled transmission of moisture produced through perspiration or enters from the outside environment. One system which meets these requirements is the Eskimo mukluk. This mukluk has an upper shell and a lower sole. The upper shell of the mukluk may be formed of soft leather, canvas or fabric, all of which are non-waterproof and necessarily breathable to permit moisture from perspiration to escape. The shell also provides sufficient insulation thickness. The mukluk soles, on the other hand, are waterproof and may be formed of animal hides. Thus, this combination keeps the foot dry as well as warm. A fur ruff is usually attached around the top of the mukluk to prevent snow from entering the footwear.
An accepted and successful improvement over the Eskimo mukluk was developed by adapting modern materials for those materials used by the Eskimos. Those changes included using: (1) soles from large overshoes or Army surplus winter footgear instead of tough animal hides for the mukluk bottoms; (2) nylon, polyester, or other breathable (but not waterproof) cloth instead of soft leather or canvas for the upper shells; and (3) a separate non-preformed "sock" for thermal insulation folded from a circular, square, or rectangular piece of 3/4 to 11/4-inch, low-density polyurethane foam. However, that system has certain disadvantages. Specifically, that system, because of its express requirement for a "breathable," non-waterproof, outer shell resulted in both poor wind resistance and water repellency. Also, folding the foam sheet around the foot and then fitting the covered foot into the shell are difficult tasks to accomplish. In addition, the foam sheet tends to abrade and compact with use and must be unfolded and rotated regularly in order to retain its effectiveness. Furthermore, the mukluk of that system provides very little support to the wearer for stability and maneuverability. Finally, moisture from the wearer's foot may accumulate and freeze in the materials between the bottom of his foot and the inside of the sole, thereby reducing the effectiveness of the underfoot insulation. All of this is inconsistent with the idea of providing modern integrated cold weather footwear.